The present investigation is an attempt to assess the strength of cortical bone structure in vivo through the utilization of three independent measurements made on normal volunteers and patients. One is a photon absorption technique which determines bone mineral content (gram of bone/running cm.), the second is the measurement of the speed of ultrasound in a transverse direction of the cortical bone, and the third is a radiograph of the bone to determine the cortical thickness and overall bone width. With the use of a bone model, additional parameters can be derived, e.g. modulus of elasticity and compact bone density. Correlation studies will be made of the parameters of cortical bone measured by our methods with radiographic evidence of bone morphology (dorsal and lumbar spine) in patients referred with bone and joint symptoms from the Orthopedic Clinic at UCLA. Correlation studies of the parameters of cortical bone will also be made with selected groups of patients with diagnoses already estabished clinically - namely proved osteoporotics and a group of patients with chronic renal disease accompanied by bone changes.